Development of new pressure-swing adsorption processes: Combination cycles, CZPSA, and SMB/PSA hybrids

Kyle Phillip Kostroski, Purdue University

Abstract

New pressure-swing adsorption (PSA) processes and PSA hybrids are developed for several commercially relevant gas separations. The Combination Cycles and Cycling-Zone Pressure-Swing Adsorption (CZPSA), respectively, use feed purge to supplement and replace product purge and are high recovery alternatives to the Skarstrom Cycle when lower product purities are acceptable. For air separation, the Skarstrom Cycle produces ∼88% O2 with pressurized O2 recovery of ∼44% while CZPSA produces ∼72% O2 with pressurized O2 recovery of 75% at the same productivity. To achieve high purity O2 and N2, CZPSA is coupled with cryogenic distillation to form a hybrid air separation process. By removing excess N2, the CZPSA unit decreases the size of downstream equipment, thereby decreasing costs. When capital costs dominate, placing the CZPSA unit after the main air compressor (MAC) in a hybrid air separation plant reduces capital cost by up to ∼27%, but power increases by ∼16%. When both capital and operating costs dominate, placing the CZPSA unit before the MAC reduces operating cost by up to ∼7% and capital costs by up to ∼9%. An existing 1000 mtpd air separation plant can be retrofitted with a pre-MAC CZPSA unit to increase the plant capacity by ∼12% with a 6% increase in incremental capital costs and a 55% increase in incremental operating costs. For dilute binary gas separation, hybrid SMB/PSA processes are developed by combining stripping-type PSA with a gas-phase SMB. As conceived, SMB/PSA has two advantages: low pressure purge and internal desorbent generation. For the two-zone, two-train SMB/PSA process, binary separation of enflurane into its 99% pure R- and S-enantiomers is achieved at D/F ∼15.0; the gas-phase SMB achieves this with D/F ∼54.0. Stripping- and rectifying-type PSA typically are not used to achieve complete binary separation because of low productivities. The gas-phase SMB is combined with these processes to achieve binary separation of a concentrated feed of H2 and CH4 with zeolite 5A. An eight-bed combination of stripping- and rectifying- type SMB/PSA processes produces 99.99% H2 with 99.6% H2 recovery and 99% CH4 with 99.9% CH4 recovery with productivity of 9.37E-5 mol/kg-s and an energy requirement of 260.9 kJ/mol.

Degree

Ph.D.

Advisors

Wankat, Purdue University.

Subject Area

Chemical engineering

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